1. Field of the Invention
The present invention relates to a method of evaluating a silicon wafer, in particular to an evaluating method suitable for judging the quality of the mirror-polishing process of a silicon wafer.
2. Description of the Related Art
Semiconductor devices usually use a silicon wafer having at least one mirror-polished surface, which is obtained by slicing a silicon single crystal manufactured by the CZ method or the FZ method, chamfering the periphery thereof, and then grinding, lapping and polishing the surface or the reverse surface thereof.
However, the grinding and polishing applied to the silicon wafer for the purpose of mirror-polishing cause damage to the wafer surface. The damage is a local residual strain that can not be distinguished visually. According to the manufacturing method of semiconductor silicon wafers disclosed in JP-A 8-70009 (JP-A: Unexamined Japanese patent publication), whether a damage is caused can be ascertained by applying selective etching to the silicon wafer and then observing with a microscope. Moreover, the damage can be eliminated by applying a short-period low-temperature heat treatment to the silicon wafer.
The above-mentioned method of manufacturing a silicon wafer is a method of eliminating the damage on the surface of the silicon wafer caused by the mirror-polishing process. Whether the quality is good can be ascertained by the selective etching. However, even applying selective etching to the silicon wafer, it is difficult to evaluate the degree of the damage, i.e, the quality of the mirror-polishing process. In particular, the relationship of the degree of damage with the quality of the electrical characteristics such as oxide film insulation, which is an important quality characteristic to the semiconductor devices, can not be ascertained.
According to the manufacturing method of semiconductor silicon wafers disclosed in JP-A-8-124984, a method of detecting a fraction defect of breakdown voltage,
discloses the steps of: dipping a mirror-polished silicon wafer in a dilute hydrofluoric acid;
washing the surface of the silicon wafer;
subjecting the surface-washed silicon wafer to a heat treatment in an oxygen atmosphere to form a thermal oxidation film;
forming a predetermined number of polycrystalline silicon electrodes having a predetermined area on the thermal oxidation film;
applying a voltage to each electrode between the predetermined number of polycrystalline silicon electrodes and the silicon wafer; and
measuring the breakdown voltage.
According to the method, octahedral oxygen precipitation defect is selectively solved in many kind of defects which are near the surface of the silicon wafer, thereby the breakdown voltage is made lower, and therefore an average density of the octahedral oxygen precipitation can be presumed more accurately.
According to the method, an average density of the octahedral oxygen precipitation is calculated and presumed based on a value obtained by detecting a fraction defect of breakdown voltage. However according to the method only average density of the octahedral oxygen precipitation is obtained but it is impossible to distinguish a deterioration caused by the crystal defect from a defect of breakdown voltage of oxidation film caused by mirror polishing process.
Whether damage is caused or notice can be ascertained by applying selective etching to the silicon wafer and then observing with a microscope. Moreover, the damage can be eliminated by applying a short-period low-temperature heat treatment to the silicon wafer.